What is pre method in mongoose?

pre(‘remove’) , Mongoose registers updateOne and deleteOne middleware on Query#updateOne() and Query#deleteOne() by default. This means that both doc. updateOne() and Model. updateOne() trigger updateOne hooks, but this refers to a query, not a document.

What is pre and post in mongoose?

Middleware (also called pre and post hooks) are functions which are passed control during execution of asynchronous functions. Middleware is specified on the schema level and is useful for writing plugins. Mongoose 4.

What is validation in mongoose?

Validation occurs when a document attempts to be saved, after defaults have been applied. Mongoose doesn’t care about complex error message construction. Errors have type identifiers. Validation is asynchronously recursive: when you call Model#save , embedded documents validation is executed.

What is required in mongoose?

Mongoose has several built-in validators. All SchemaTypes have the built-in required validator. Numbers have min and max validators. Strings have enum , match , minLength , and maxLength validators.

What are the rules for validation in mongoose?

Before we get into the specifics of validation syntax, please keep the following rules in mind: Validation is middleware. Mongoose registers validation as a pre (‘save’) hook on every schema by default. You can manually run validation using doc.validate (callback) or doc.validateSync () Validators are not run on undefined values.

How does the save function work in mongoose?

The save() function triggers validate() hooks, because mongoose has a built-in pre(‘save’) hook that calls validate(). This means that all pre(‘validate’) and post(‘validate’) hooks get called before any pre(‘save’) hooks.

Can you access the document being updated in mongoose?

You cannot access the document being updated in pre (‘updateOne’) or pre (‘findOneAndUpdate’) query middleware. If you need to access the document that will be updated, you need to execute an explicit query for the document. However, if you define pre (‘updateOne’) document middleware, this will be the document being updated.

How does pre and post hooks work in mongoose?

All middleware types support pre and post hooks. How pre and post hooks work is described in more detail below. Note:If you specify schema.pre(‘remove’), Mongoose will register this middleware for doc.remove()by default. If you want to your middleware to run on Query.remove()use schema.pre(‘remove’, { query: true, document: false }, fn).